Cellular Division
I. Introduction
• According to the CELL THEORY, new cells
are only produced by existing cells…
THUS, cell division is essential for the
continuation of life!
• Why do cells DIVIDE?
1. Maintain Homeostasis
2. Reproduction: create new,independent
organisms (i.e. prokaryotes)
 divide by binary fission
3. Growth and repair of damage cells
(e.g. next slide)
 About 2 trillion cells are produced by an
adult human body every day.
 These new cells are formed when
older cells REPRODUCE (i.e. divide),
which is known as CELL DIVISION.
 When cells divide, the DNA is:
1. replicated (i.e. copied)
2. distributed
- each new cell receives a complete
set (copy) of parent DNA
 Cell Division involves DIFFERENTIATION
Differentiation is the process by which
cells grow into specialized tissues
When cells differentiate, they develop
specific structures or contain more of a
certain organelle that allow them to
perform particular functions in the body
Example:
- RBC’s have large amount of hemoglobin enabling
them to carry large amts of O2
- Nerve cells have special receptors to react to stimuli
and conduct impulses
- Muscle cells have large amounts of mitochondria for
extra ATP production
Cell Differentiation
 Differentiation involves SPECIALIZATION
- Due to the complexity of multicellular
organisms, cells must become highly
organized, in which their cells perform
specific functions
- It means that every cell doesn’t perform
the exact same function all of the time,
this would waste NRG
- Thus, cells can shut off certain genes:
lung cells don’t need proteins used by liver
hair cells don’t need dental enamel
Cell Specialization
 There are two phases of cell division:
1. Nuclear Division
a. division of the genetic material
(i.e. nucleus)
b. two types:
1. Mitosis – produces two
genetically identical nuclei
2. Meiosis – produces 4 nuclei
w/ half the genetic material
as the original cell
2. Cytoplasmic Division (Cytokinesis)
 divides the cytoplasmic contents
II. VOCABULARY!!!!!
A. Chromatin – The “uncoiled” complex of
DNA wrapped around proteins
(similar to plate of tangled spaghetti)
1. Histones – 8 proteins that form
a core that DNA wraps itself
around. Why does DNA do this?
 It’s too large, needs to be
wound up to fit into nucleus
2. Nucleosome – the complex of
DNA wrapped around histones
 strung together like a thin
strand of beads
B. Chromatid –
1. A single strand of tightly coiled up
chromatin
C. Chromosome 1. A tightly coiled structure of DNA
and proteins which contains genes
2. When DNA replicates; chromosomes
consist of 2 chromatid strands
(i.e. sister chromatids, exact copies)
 centromere – the region on a
chromosome where sister chromatids
are attached
III. Chromosome #
A. Humans contain two types of cells:
1. SEX CELLS (a.k.a. gametes)
 the egg and sperm
2. SOMATIC CELLS (a.k.a. body cells)
 Any cell that is not egg or sperm
B. Humans have 2 types of chromosomes:
1. sex chromosomes (i.e. X and Y)
2. autosomes – all other chromosomes
C. Sets of chromosomes
1. Every human somatic cell has 2 SETS
(i.e. copies, 1 from MOM & 1 from DAD)
of 23 different chromosomes
 23 pairs of Homologous chromosomes
(identical in size, shape, genetic info,
genes found in same location)
- 22 pairs of autosomes
- 1 pair of sex chromosomes
 TOTAL = 46 CHROMOSOMES
2. Every human sex cell has only ONE SET
of chromosomes (i.e. 23 TOTAL)
 Sex cells fuse together during
FERTILIZATION to form a ZYGOTE,
which now has 46 chromosomes.
3. PLOIDY Levels
 represents the number of complete
sets of chromosomes present in an
organism’s cells.
a. Sex cells (i.e. gametes) are:
 HAPLOID (n) = 23 chromosomes
b. Somatic cells are:
 DIPLOID (2n) = 46 chromosomes
What about strawberries?
Octoploid (8n)
4. KARYOTYPE – a photograph that shows
the 23 sets of chromosomes arranged
by size
22 pairs autosomes
1 pair sex-chrom.
D. Changes to chromosomes (Disorders)
1. Disorders can result from STRUCTURAL
mutations (discuss this later…genetics)
2. Disorders can result from mutations in
NUMBER (i.e. extra chromosomes). Ex…
IV. The Cell Cycle
A. Background
 Cells are not always engaged
in division; cells go thru
different stages of life…
 some cells’ division is ongoing
(e.g. stem cells – skin, bone,
bone marrow)
 some cells lose ability to divide
(e.g. muscle, neurons, RBC’s)
B. Overview of Cell Cycle
1. Definition – the orderly events in the
lifetime of a cell
2. One cycle is the period b/n a cells
creation by mitosis and its subsequent
division into two new daughter cells.
3. Broken into two phases:
a. INTERPHASE – the longer period b/n
divisions
1. G1 phase – Growth; normal activity
2. S phase – DNA synthesis
3. G2 phase – Preparation for division
b. MITOSIS & CYTOKINESIS – nuclear &
cytoplasmic division
C. Two main stages:
1. Interphase
a. cells are NOT dividing
b. eukaryotic cells spend most of
their life in this stage
c. the cell does normal tasks
associated w/ its specialized
fxns and maintenance
d. DNA in the form of chromatin
e. three phases: G1, S, G2
* the three phases of interphase:
G1 (gap/growth 1):
 DNA is relaxed & unreplicated (chromatin)
in order to direct normal cell activity
(e.g. protein synthesis)
 organelles are duplicated
 G1 checkpoint – ensures that everything
is ready for synthesis
 S-cyclins – proteins that help activate
a protein complex called MPF. An active
MPF then activates multiple other
enzymes in a cascade effect. This
essentially signals DNA to move into the
next phase (synthesis/replication)
S phase (DNA Synthesis)
 all 46 chromosomes and the DNA
they contain will be replicated
 each chromosome is now
composed of sister chromatids
 MPF will begin to degrade the
S-cyclins and once again becomes
inactive
G2 (gap/growth 2)
 the cell “double checks” the
duplicated chromosomes and other
contents & repairs any errors
 G2 checkpoint – ensures the cell is
ready for mitosis
 M-cyclins will activate a different
MPF complex, creating another
cascade which tells the cell
to move into the final phase
(i.e. mitosis)
2. Mitosis
 the contents of the nucleus will
be divided into 2 genetically
identical daughter cells
 M checkpoint – ensures that cell
is ready to complete division
 MPF will degrade the M-cyclins
and become inactive
 cells re-enter G1 phase after
finish dividing
G0 (gap/growth 0)
 Cells that cease cell division will
enter this phase and remain
there until cell death (e.g. RBC)
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation_
_how_the_cell_cycle_works.html
SOMATIC cells)
V. Mitosis (nuclear division of ________
 Definition – the replication & division of
ONE PARENT NUCLEUS into 2 IDENTICAL
DAUGHTER NUCLEI, each receiving an
EXACT COPY of parent’s chromosomes.
A. Preparation for mitosis  Interphase
1. nuclear envelope & nucleolus intact
2. “uncoiled” chromatin
3. centrosomes w/ centrioles form (this
will direct chromosome mov’t)
B. Phases of Mitosis (5 total)
1. Prophase: longest
* centrosomes move toward opposite poles
* spindle fibers begin to form
* chromatin coils tightly (chromosomes now
visible; 2 sister chromatids)
Early prophase
Late Prophase:
* kinetochores develop on centromeres
(this is where spindle fibers will attach)
2. Prometaphase
* nuclear envelope & nucleolus dismantle
* spindle fibers attach to kinetochores
and begin moving chromosomes toward
center of cell
3. Metaphase
* all chromosomes are aligned in the
in the center of the cell (equatorial plate)
4. Anaphase
* centromeres divide
* spindles shorten & pull chromatids apart
* each chromatid, now a daughter
chromosome, moves to opposite poles
* “V-shaped” (centromeres being pulled)
(20 ATP)
5. Telophase
* chromosomes reach poles & spindles
break down
* chromosomes “uncoil” to form chromatin
* nuclear envelope & nucleolus reform
C. Post mitosis Cytokinesis (cytoplasm divides)
* The membrane pinches together forming
a cleavage furrow.
* Keep contracting until 2 new cells
 In ANIMALS – cell membrane pinches
together to form a cleavage furrow
 In PLANTS – vesicles form at midline &
extend outward forming a cell plate.
A new cell wall forms on both sides.
http://highered.mcgrawhill.com/sites/9834092339/student_view
0/chapter10/animation__cell_division.html
http://www.iknow.net/player_window.html?url=media/prophase_vi
deo_auto.swf&width=360&height=285
http://www.iknow.net/player_window.html?url=media/plant_mitosis_aut
o.swf&width=360&height=285
http://bcs.whfreeman.com/thelifewire/content/chp0
9/0902001.html
Test Your Knowledge
Telophase
Metaphase
Anaphase
Cytokinesis
Prophase
metaphase
cytokinesis
prometaphase
prophase
anaphase
interphase
VI. Cancer
 A cell loses control over its own division
 they divide rapidly and inappropriately
A. How cancer develops (3 main ways)
1. Mutation in proto-oncogene
- these genes code for growth factors, which
are proteins that regulate cell division
- mutation will turn them into oncogenes
causing unregulated/extreme cell division
2. Mutation of tumor-suppressor genes
- found in over half of all cancer cases
- p53 is one such gene which encodes a
protein that halts cell cycle before division
to allow damaged DNA to be repaired…
cell undergoes apoptosis-cell death, good!!
If faulty p53, cell cycle will not halt and
damaged cells will multiply  tumors
They invade normal tissue and destroy it.
p53 — master regulator gene
NORMAL p53
p53
protein
p53
protein
Step 2
Step 1
Step 3
ABNORMAL p53
Abnormal
p53 protein
Step 1
DNA damage is
caused by heat,
radiation, or
chemicals.
Cancer
cell
Step 2
The p53 protein fails to stop
cell division and repair DNA.
Cell divides without repair to
damaged DNA.
Step 3
Damaged cells continue to divide.
If other damage accumulates, the
cell can turn cancerous.
3. Lack of APOPTOSIS (programmed cell death)
- Normally, your body sends a signal to your
cells to kill themselves when:
1. they need to develop (webbed hands)
2. they become infected w/ virus
3. they begin to grow abnormally and DNA
mutation can’t be fixed (tumors)
- Cancer cells don’t receive the signals
triggering apoptosis (radiation forces apop.)
Development of Cancer

Cancer develops only after a cell
experiences ~6 key mutations

unlimited growth


ignore checkpoints


turn on chromosome maintenance genes
promotes blood vessel growth


turn off suicide genes
immortality = unlimited divisions


turn off tumor suppressor genes
escape apoptosis


turn on growth promoter genes
turn on blood vessel growth genes
overcome anchor & density dependence

turn off touch censor gene
B. Different forms:
1. carcinomas: lung, breast, colon, liver
2. sarcomas: bone, muscle
3. lymphoma/leukemia: WBC’s & RBC’s
C. Causes:
1. carcinogens – chemicals that cause mutations
in DNA (e.g. radiation, smoke, pesticides)
D. Metastasis
1. the spreading of cancer cells from point of
origin to other parts of the body:
2. Moves by way of lymphatic system
(surgery can remove lymph nodes)
REVIEW - HUMANS HAVE:
diploid
46 Diploid or haploid? __________
How many chromosomes? _____
2
How many complete sets of chromosomes? _____
23 Diploid/haploid? haploid
How many chromosomes in a set? _____
_______
23 In a somatic cell?____
46
How many chromosomes in a gamete? _____
23
How many pairs of homologous chromosomes? _____
2
How many sex chromosomes? _____
44
How many autosomes? _____
22
How many pairs of autosomes? _____
1
How many pairs of sex chromosomes? _____